Avi

Splitting AVI's with mencoder

mencoder -ovc copy -oac copy -ss 56:54 -endpos 11:07 -o output.avi input.avi

-ss Start Position
-endpos End Position

Combining AVI's with mencoder

First, combine the two AVI's via shell redirection:

cat file1.avi file2.avi >> output.avi

Next, re-encode the file so that things are synced properly:

mencoder -forceidx -oac copy -ovc copy infile.avi -o outfile.avi

Re-encoding MPG to AVI format

mencoder

This is an untested solution:

input_filename.mpg
-ovc codec for video output
-oac codec for audio output
-o output_filename.avi

mencoder <filename.avi> -ovc lavc -oac lavc -o <output.avi> 

Transcode

-i input_filename.mpg

-y codec for audio/video output
-o output_filename.avi

transcode -i movie.mpg -o movie.avi -y xvid